In the field of medicine, imaging and image guidance are a significant component of clinical care. From diagnosis and monitoring of disease, to planning of the surgical approach, to guidance during procedures and follow-up after the procedure is complete, imaging and image guidance provides effective and multifaceted treatment approaches, for a variety of procedures, including surgery and radiation therapy. Targeted stem cell delivery, adaptive chemotherapy regimes, and radiation therapy are only a few examples of procedures utilizing imaging guidance in the medical field.
Advanced imaging modalities such as Magnetic Resonance Imaging (“MRI”) have led to improved rates and accuracy of detection, diagnosis and staging in several fields of medicine including neurology, where imaging of diseases such as brain cancer, stroke, Intra-Cerebral Hemorrhage (“ICH”), and neurodegenerative diseases, such as Parkinson's and Alzheimer's, are performed. As an imaging modality, MRI enables three-dimensional visualization of tissue with high contrast in soft tissue without the use of ionizing radiation. This modality is often used in conjunction with other modalities such as Ultrasound (“US”), Positron Emission Tomography (“PET”) and Computed X-ray Tomography (“CT”), by examining the same tissue using the different physical principals available with each modality. CT is often used to visualize boney structures and blood vessels when used in conjunction with an intra-venous agent such as an iodinated contrast agent. MRI may also be performed using a similar contrast agent, such as an intra-venous gadolinium based contrast agent which has pharmaco-kinetic properties that enable visualization of tumors and break-down of the blood brain barrier. These multi-modality solutions can provide varying degrees of contrast between different tissue types, tissue function, and disease states. Imaging modalities can be used in isolation, or in combination to better differentiate and diagnose disease.
In neurosurgery, for example, brain tumors are typically excised through an open craniotomy approach guided by imaging. The data collected in these solutions typically consists of CT scans with an associated contrast agent, such as iodinated contrast agent, as well as MRI scans with an associated contrast agent, such as gadolinium contrast agent. Also, optical imaging is often used in the form of a microscope to differentiate the boundaries of the tumor from healthy tissue, known as the peripheral zone. Tracking of instruments relative to the patient and the associated imaging data is also often achieved by way of external hardware systems such as mechanical arms, or radiofrequency or optical tracking devices. As a set, these devices are commonly referred to as surgical navigation systems.
Three dimensional (3D) sensor systems are increasingly being used in a wide array of applications, including medical procedures. These sensor systems determine the shape and/or features of an object positioned in a scene of the sensor system's view. In recent years, many methods have been proposed for implementing 3D modeling systems that are capable of acquiring fast and accurate high resolution 3D images of objects for various applications.
Triangulation based 3D sensor systems and methods typically have one or more projectors as a light source for projecting onto a surface and one or more cameras at a defined, typically rectified relative position from the projector for imaging the lighted surface. The camera and the projector therefore have different optical paths, and the distance between them is referred to as the baseline. Through knowledge of the baseline distance as well as projection and imaging angles, known geometric/triangulation equations are utilized to determine distance to the imaged object. The main differences among the various triangulation methods known in the art lie in the method of projection as well as the type of light projected, typically structured light, and in the process of image decoding to obtain three dimensional data.
A 3D sensor system may be contemplated as a novel extension of a surgical navigation systems. One popular triangulation based 3D sensor system is created by Mantis Vision, which utilizes a single frame structured light active triangulation system to project infrared light patterns onto an environment. To capture 3D information, a projector overlays an infrared light pattern onto the scanning target. Then a digital camera and a depth sensor, synched to the projector, captures the scene with the light reflected by the object. The technology works even in complete darkness, since it includes its own illumination; in bright environments the quality of the resulting image depends on the hardware used.
During a medical procedure, navigation systems require a registration to transform between the physical position of the patient in the operating room and the volumetric image set (e.g., MRI/CT) being navigated to. Conventionally, this registration is done to the position of a reference tool, which is visible by the tracking system and stays fixed in position and orientation relative to the patient throughout the procedure.
This registration is typically accomplished through correspondence touch points (e.g., either fiducial or anatomic points). Such an approach to registration has a number of disadvantages, including requiring fiducials to be placed before scans, requiring points to be identified, providing for a limited number of points, touch point collection is subject to user variability, and the physical stylus used for collecting the points can deform or deflect patient skin position. Another conventional approach to collecting the touch points includes performing a surface tracing of the patient drawn as a line which is matched to the image set surface contour using either a stylus pointer or a laser pointer. Such an approach to registration has a number of disadvantages, including providing for a limited number of points, and the physical stylus can deform or deflect patient skin position. Yet another conventional approach to collecting the touch points includes using a mask, which requires a high level of operator training and is operator dependent. This approach also provides only a limited number of points.
Other common limitations of the conventional approaches to registration discussed above include a stylus that needs to remain visible to the tracking system, which not necessarily possible depending on a patient's surgical position or may introduce surgical restrictions that need to be accounted in planning, and error accumulation where touch point or tracing collection is of low quality resulting in error propagation through subsequent steps of the registration. Further, using the conventional methods, if registration is lost, re-registration is difficult if not possible to be completed again during surgery.
Therefore, there is a need for an improved system and method for mapping navigation space to patient space in a medical procedure.